MPPT Charge Rate

Well… I have been amazed.

I moved 1 string (3x 540w panels) to my 150/60 to see how much I was being throttled on the 250/85 (3s3p 540w)
Before: 250/85 (3s3p) - Max charge current 85a (Max 4400 w from 4850w string)
Now (yesterday):

  • 250/85 (2s3p)= PMax: 4500w / Battery IMax 85.5a (clipped?)
  • 150/60 (1s3p) = PMax: 2145w / Battery IMax 41.1a

So theoretical max yield 4850 is actually 6645w. (Cloud effect maybe but not much as it was a clear day)

I was missing out on an extra 35a charge current to my battery with the “to small” MPPT.

I’m happy!


These Victron MPPTs are really fantastic.

Many people forget that the max power output is the battery voltage x the current limit of the MPPT and you showed it nicely in this example.

This is also where a 16S battery will give you a higher max power than 15S.
15S: 3.4Vx15=51V x 85A = 4335W
16S: 3.4Vx16=54.4V x 85A = 4624W

So as long as you have enough watts on the PV side for supply, that would be your conversion. Naturally if your battery is close to empty the voltage drops and your max PV also drops.
15S: 3.0Vx15=45V x 85A = 3825W
16S: 3.0Vx16=48V x 85A = 4080W

Thus on the same MPPT and PV your battery can limit your power output by 600W if the battery is empty and another 300W if you use a 15S vs 16S battery

PS. I have ignored any degraded output on the PV side (warm/cold panels) - if your PV power is less than these max values then that would be the limiting factor.

Also recently saw how amazing these MPPT’s are.

Simple example.

The best I have been able to extract is about 3800W from a 5000W array. My strings are such that the max volts I’ve ever recorded was 111V and 121V respectively from 2 x 150 | 35 MPPT which is still far from their limits.

My mother on the other hand with her new Luxpower installation has a theoretical 2775W array, and I’ve seen 2300W extracted (and this was with the battery very close to full).

I can only assume that this is because of the much higher volts from 5 x 555W panels in serie. Unfortunately the Luxpower app does not show amps which I like more to gauge a system’s performance.

But her losses are just over 10% whereas mine is closer to 25%

I regularly can exceed the max of my array. Sometimes by 15% so always surprised! These are spikes though but still good numbers.
9200 from a 8110 array.

Batteries full by 10am (from 34%, 14.5 kw bank)

That’s really amazing! I suppose I’ll only see such performance once I upsize my MPPT’s and put more panels in serie.